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United States Patent |
5,215,851
|
Tomita
,   et al.
|
June 1, 1993
|
Electrophotographic toner
Abstract
A toner comprising capsule particles composed of a core and an outer shell
wherein the capsule particles have at least a substance capable of forming
a radical at the surface thereof, and the capsule particles have adhered
on the outer shell a copolymer comprising a hydrophilic vinyl monomer unit
and a hydrophobic vinyl monomer unit. The toner exhibits stable
chargeablity against environmental changes with a narrow charge
distribution.
Inventors:
|
Tomita; Kazufumi (Kanagawa, JP);
Inaba; Yoshihiro (Kanagawa, JP);
Takashima; Koichi (Kanagawa, JP)
|
Assignee:
|
Fuji Xerox Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
754662 |
Filed:
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September 4, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
430/110.2; 430/137.11; 430/138 |
Intern'l Class: |
G03G 009/00; G03G 005/00; G03C 001/72 |
Field of Search: |
430/109,110,904,138,137
|
References Cited
U.S. Patent Documents
4597794 | Jul., 1986 | Ohta et al. | 106/20.
|
4761358 | Aug., 1988 | Hosoi et al.
| |
Foreign Patent Documents |
59-185353 | Oct., 1984 | JP.
| |
59-187350 | Oct., 1984 | JP.
| |
59-187352 | Oct., 1984 | JP.
| |
59-187355 | Oct., 1984 | JP.
| |
59-187357 | Oct., 1984 | JP.
| |
59-189354 | Oct., 1984 | JP.
| |
59-189355 | Oct., 1984 | JP.
| |
Primary Examiner: McCamish; Marion E.
Assistant Examiner: Crossan; Steve
Attorney, Agent or Firm: Finnegan, Henderson, Farabow, Garrett & Dunner
Claims
What is claimed is:
1. A toner comprising capsule particles composed of a core and an outer
shell wherein said capsule particles have at least a substance capable of
forming a radical at the surface thereof, and said capsule particles have
adhered on the outer shell a copolymer comprising a hydrophilic vinyl
monomer unit and a hydrophobic vinyl monomer unit.
2. The toner as claimed in claim 1, wherein said substance capable of
forming a radical is selected from the group consisting of polyamide,
polyurea, polyurethane, polyester, polyvinyl acetate, polyvinyl alcohol,
cellulose, synthetic rubbers, polystyrene, acrylate copolymers,
methacrylate copolymers, styren-acrylate copolymers, styrene-methacrylate
copolymers, epoxy resins, phenoxy resins, and acrylic resins, and a
mixture thereof.
3. The toner as claimed in claim 1, wherein said copolymer is adhered on
the capsule particles through graft polymerization.
4. The toner as claimed in claim 1, wherein at least one of said
hydrophilic vinyl monomer unit and said hydrophobic vinyl monomer unit
contains a charge control group.
5. The toner as claimed in claim 4, wherein said charge control group is
selected from the group consisting of an ammoniumyl group, an amino group,
an amido group, a trialkylsilane group, a trialkoxysilane group, a halogen
atom, a carboxyl group, a sulfo group, a cyano group, and a hydroxy group.
6. The toner as claimed in claim 1, wherein the proportion of said
hydrophilic vinyl monomer unit is from 0.01 to 50 mol % based on the total
monomer unit of the copolymer.
Description
FIELD OF THE INVENTION
This invention relates to a toner for visualizing an electrostatic latent
image in electrophotography or electrostatic printing.
BACKGROUND OF THE INVENTION
Conventional techniques for controlling charging properties of toners
include incorporation of a charge control agent, e.g., nigrosine, into
toner particles by melt-kneading.
It has been proposed to conduct charge control by adhering a polymer, such
as an acrylonitrile polymer, a polymer having an aminophenylthio group,
and a polymer of a diallylammonium halide, to the surface of the core of
toner particles as disclosed in JP-A-62-106474 (the term "JP-A" as used
herein means an "unexamined published Japanese patent application"),
JP-A-60-26347, and JP-A-60-26346.
Toners having a charge control function on the surface thereof further
include those in which a vinylpyridine polymer or a vinylimidazole polymer
is present on the surface of core particles, those in which a polymer of a
compound having a tertiary amine in the molecule thereof is present on the
surface of core particles, and those in which a polymer of
(meth)acrylonitrile, (meth)acrylic acid, vinyl fluoride, methyl
methacrylate, vinylcarbazole, vinylpyridine, dimethylaminoethyl
methacrylate, diacetoneacrylamide, or N-vinylimidazole is present on the
surface of core particles, as disclosed in JP-A-62-227161, JP-A-62-227162,
JP-A-63-177145, JP-A-63-177147, and JP-A-63-177148.
Where a charge control agent is incorporated into toner particles, since it
is only the agent present on the outer surface of toner particles that
takes part in charge control, the agent must be used in large quantity.
On the other hand, where a charge control function is performed by a charge
controlling polymer present on the surface of core particles, charging
properties of the toner are dependent on the environmental conditions,
particularly humidity because the monomer unit constituting the charge
controlling polymer contains both a hydrophilic group and a charge control
group per molecule. When a monomer containing both a hydrophobic group and
a charge control group per molecule is used, environmental stability of
the charging properties is improved, but the resulting toner shows a
greatly broadened charge distribution.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a toner whose charging
properties are little dependent on environmental conditions and having a
narrow charge distribution.
The object of the present invention is accomplished by a toner comprising
capsule particles composed of a core and an outer shell, wherein said
capsule particles have at least a substance capable of forming a radical
at the surface thereof and, said capsule particles have adhered on the
outer shell a copolymer comprising a hydrophilic vinyl monomer unit and a
hydrophobic vinyl monomer unit.
DETAILED DESCRIPTION OF THE INVENTION
The terminology "substance capable of forming a radical" as used herein
means a substance which undergoes a hydrogen attraction or addition
reaction with a monomer radical or cerium (IV) ion to form a radical.
Specific examples of such a substance include polyamide, polyurea,
polyurethane, polyester, polyvinyl acetate, polyvinyl alcohol, cellulose,
synthetic rubbers, polystyrene, acrylate or methacrylate (hereafter
collectively referred to as "(meth)acrylate") copolymers,
styrene-(meth)acrylate copolymers, epoxy resins, phenoxy resins, and
acrylic resins, and mixtures of these polymers.
The substance capable of forming a radical may be uniformly present either
on the entire surface of the outer shell before application of the
copolymer or in spots. Alternatively, the substance may constitute the
outer shell of capsule particle.
The terminology "hydrophilic vinyl monomer" as used herein means a vinyl
monomer having a water solubility of at least 10 and preferably 20 or
more. The term "water solubility" herein used means a maximum amount
(grams) of solute to be dissolved in 100 g of water at 20.degree. C.
Specific examples of such a monomer include (meth)acrylic acid or a metal
salt thereof, ethyltrimethylammonium chloride (meth)acrylate,
ethyltriethylammonium chloride (meth)acrylate,
triethyl(p-vinylbenzyl)ammonium chloride, trimethyl(p-vinylbenzyl)ammonium
chloride, t-butylacrylamide, ethylbenzyldimethylammonium chloride
(meth)acrylate, acrylonitrile, methacrylonitrile, vinylimidazole,
acrolein, acrylamide, methacrylamide, allyl alcohol, methallyl alcohol,
allylamine, methallylamine, diallylamine, 2-methacryloyloxyethylsuccinic
acid or a metal salt thereof, ethylenesulfonic acid or a metal salt
thereof, fumaric acid or a metal salt thereof, itaconic acid or a metal
salt thereof, maleic acid or a metal salt thereof, vinylacetic acid or a
metal salt thereof, and styrenesulfonic acid or a metal salt thereof.
Examples of the metal salts as described above include sodium salts,
potassium salts, carcium salts, magnecium salts and zinc salts which have
the water solubility of at least 10.
The terminology "hydrophobic vinyl monomer" as used herein means a vinyl
monomer having the water solubility of less than 10 and preferably 5 or
less. Specific examples of such a monomer include vinylidene chloride;
allyl chloride and methallyl chloride; (meth)acrylates, e.g., methyl
(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl
(meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, lauryl
(meth)acrylate, trifluoroethyl methacrylate, cyclohexyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, hydroxyethyl
(meth)acrylate, hydroxypropyl (meth)acrylate, 2-ethoxyethyl
(meth)acrylate, glycidyl (meth)acrylate, and phenyl (meth)acrylate;
vinyl-containing cyano compounds, e.g., cyanostyrene; fatty acid vinyl
esters, e.g., vinyl formate, vinyl acetate, vinyl chloroacetate, vinyl
propionate, vinyl butyrate, vinyl trimethylacetate, vinyl benzoate, vinyl
caproate, vinyl caprylate, and vinyl stearate; vinyl ethers, e.g., ethyl
vinyl ether, propyl vinyl ether, butyl vinyl ether, hexyl vinyl ether,
2-ethylhexyl vinyl ether, and phenyl vinyl ether; vinyl ketones, e.g.,
phenyl vinyl ketone; and vinyl aromatic compounds, e.g., styrene,
chlorostyrene, hydroxystyrene, .alpha.-methylstyrene, and vinylpyridine.
In the present invention, a charge control group must be present on either
one or both of the above-described hydrophilic vinyl monomer and
hydrophobic vinyl monomer. Charge control groups to be used in positively
chargeable toners include nitrogen-containing groups and
silicon-containing groups, such as an ammonium group, an amino group, an
amido group, a trialkylsilane group, and a trialkoxysilane group. Those to
be used in negatively chargeable toners include a halogen atom, a carboxyl
group, a sulfo group, a cyano group, and a hydroxy group.
Where the toner of the present invention is used as a positively chargeable
toner, it is recommended to use a vinyl monomer having a quaternary
ammonium salt structure as a charge control group.
Where the toner is used as a negatively chargeable toner, it is recommended
to use a hydrophobic vinyl monomer having a halogen atom, e.g., a fluorine
atom or a chlorine atom, as a charge control group.
The hydrophilic vinyl monomer is usually used in a proportion of from 0.01
to 50 mol %, and preferably from 0.1 to 40 mol %, based on the total with
the hydrophobic vinyl monomer. Within such a proportion, charging
properties stable against different environmental conditions and a
satisfactory charge distribution can be assured.
The terminology "adhered" as used for the relation between the surface of
capsule particles and the copolymer means that the above-described
copolymer is bonded to the surface of capsule particles through physical
or chemical bonding and does not release therefrom during development.
It is particularly preferable that the copolymer is chemically bonded to
the surface of toner particles by, for example, graft polymerization so as
not to release therefrom.
The toner of the present invention has a particle diameter usually of from
4 to 30 .mu.m, and preferably of from 6 to 18 .mu.m.
The toner of the present invention has a so-called capsule structure
composed of a core and an outer shell.
The core particles have an average particle size usually ranging from 2 to
30 .mu.m, and preferably from 4 to 18 .mu.m.
In the capsule structure, the outer shell is a very thin coating layer,
making it difficult to add therein a charge control agent. According to
the present invention, however, charge control can easily be achieved
without incorporating a charge control agent into the outer shell.
The outer shell material includes polyurea resins, polyurethane resins,
polyamide resins, polyester resins, epoxy resins, epoxyurea resins, and
epoxyurethane resins. In particular, a polyurea resin, a polyurethane
resin, an epoxyurea resin, an epoxyurethane resin, a mixture of a polyurea
resin and a polyurethane resin, or a mixture of an epoxyurea resin and an
epoxyurethane resin is preferred.
It is preferable to vary the thickness of the outer shell depending on
whether fixing is effected by pressure application or heat application
while the thickness is generally from 0.01 to 3 .mu.m. The kinds of the
constituting components or the ratio of the components may be varied for
the same purpose. For pressure fixing, the shell of the capsule usually
ranges from 0.05 to 3 .mu.m, preferably from 0.1 to 1 .mu.m, and for heat
fixing, it usually ranges from 0.01 to 3 .mu.m, preferably from 0.05 to 2
.mu.m.
The core substance of the capsule particles mainly comprises a pressure
fixable component for pressure fixing or a heat fixable component for heat
fixing. For pressure fixing, a core substance mainly comprising a binder
resin, a high-boiling solvent for dissolving the binder resin, and a
colorant and a core substance mainly comprising a soft solid substance and
a colorant are particularly preferred. If desired, the colorant may be
replaced with a magnetic powder, or for improving fixing properties
additives, e.g., silicone oil, may further be added. The high-boiling
solvent capable of dissolving the binder resin may be used in combination
with a high-boiling solvent incapable of dissolving the binder resin.
Binder resins which can be used in the core substance are selected from
known fixing resins, include acrylic ester polymers, e.g., polymethyl
acrylate, polyethyl acrylate, polybutyl acrylate, poly-2-ethylhexyl
acrylate, and polylauryl acrylate; methacrylic ester polymers, e.g.,
polymethyl methacrylate, polybutyl methacrylate, polyhexyl methacrylate,
poly-2-ethylhexyl methacrylate, and polylauryl methacrylate; copolymers of
an acrylate and a methacrylate; copolymers of a styrene monomer and an
acrylic or methacrylic ester; polyvinyl acetate, polyvinyl propionate,
polyvinyl butyrate; ethylenical polymers or copolymers, e.g., polyethylene
and polypropylene; styrene copolymers, e.g., a styrene-butadiene
copolymer, a styrene-isoprene copolymers, and a styrene-maleic acid
copolymer; polyvinyl ether, polyvinyl ketone, polyester, polyamide,
polyurethane, rubbers, epoxy resins, polyvinyl butyral, rosin, modified
rosins, terpene resins, and phenolic resins, either individually or in
combination thereof. Polymerization for preparing a binder resin may be
preceded by encapsulation.
High-boiling solvents for dissolving the binder resin include oil-soluble
solvents having a boiling point of 140.degree. C. or higher, and
preferably 160.degree. C. or higher. Such solvents may be selected from,
e.g., those listed in Modern Plastics Encyclopedia, "Plasticizers"
(1975-1976) and those known as a core substance of pressure fixable
capsule toners as disclosed in JP-A-58-145964 and JP-A-63-163373. Specific
examples of suitable high-boiling solvents are phthalic esters (e.g.,
diethyl phthalate, dibutyl phthalate), aliphatic dicarboxylic acid esters
(e.g., diethyl malonate, dimethyl oxalate), phosphoric esters (e.g.,
tricresyl phosphate, trixylyl phosphate), citric esters (e.g.,
o-acetyltriethyl citrate), benzoic esters (e.g., butyl benzoate, hexyl
benzoate), fatty acid esters (e.g., hexadecyl myristate, dioctyl adipate),
alkylnaphthalenes (e.g., methylnaphthalene, dimethylnaphthalene,
monoisopropylnaphthalene, diisopropylnaphthalene), alkyldiphenyl ethers
(e.g., o-, m-, or p-methyldiphenyl ether), higher fatty acid or aromatic
sulfonic acid amides (e.g., N,N-dimethyllauroamide,
N-butylbenzenesulfonamide), trimellitic acid esters (e.g., trioctyl
trimellitate), diarylalkanes (e.g., diarylmethanes, e.g.,
dimethylphenylphenylmethane, and diarylethanes, e.g.,
1-phenyl-1-methylphenylethane, 1-dimethylphenyl-1-phenylethane,
1-ethylphenyl-1-phenylethane), and chlorinated paraffins.
The soft solid substance which can be used as a core substance of pressure
fixable capsule toners is not particularly limited as long as it has
softness at room temperature and fixability. Preferred are polymers having
a glass transition temperature of from -60.degree. to 5.degree. C. and
mixtures of such polymers and other polymers.
Usable colorants include inorganic pigments, e.g., carbon black, red oxide,
Prussian blue, and titanium oxide; azo pigments, e.g., Fast Yellow, Disazo
Yellow, pyrazolone red, Chelate Red, Brilliant Carmine, and Para Brown;
phthalocyanine pigments, e.g., copper phthalocyanine and metal-free
phthalocyanine; and condensed polycyclic pigments, e.g., flavanthrone
yellow, dibromoanthrone orange, perylene red, quinacridone red, and
dioxazine violet. Disperse dyes and oil soluble dyes are also employable.
Examples of magnetic powders which may be used in the core include
magnetite, ferrite, and metals (e.g., cobalt, iron, nickel) or alloys
thereof.
In the preparation of capsule particles, while processes for encapsulation
are not particularly restricted, encapsulation by interfacial
polymerization is particularly preferred for facilitating sufficient
coating and for assuring sufficient mechanical strength of the outer
shell. Encapsulation by interfacial polymerization can be carried out in a
known manner, for example, by a process for incorporating one component of
the core substance into capsules in which other core components in a
previously polymerized form, a low-boiling solvent, and a shell-forming
component are charged and an outer shell is formed by interfacial
polymerization or a process in which a monomer or monomers are charged and
an outer shell is formed by interfacial polymerization and then the
monomers are polymerized to form a core substance (see JP-A-57-79860,
JP-A-58-66948, JP-A-59-148066, and JP-A-59-162562).
The effects of the present invention can be explained by the following
mechanism. Where chargeability is endowed by a hydrophilic monomer having
a charge control group, copolymerization with a hydrophobic monomer makes
the copolymer on the toner surface hydrophobic. As a result, conductivity
of the toner surface markedly reduces thereby to reduce environment
dependence, particularly humidity dependence, of chargeability. If only
the hydrophilic monomer having a charge control group is adhered on the
capsule shell, it is difficult to give a large charge quantity to the
toner particles. To the contrary, copolymerization with a hydrophobic
monomer makes it possible to endow the toner particles with high
chargeability. On the other hand, where chargeability is endowed by a
hydrophobic monomer having a charge control group, the combined use of a
hydrophilic monomer affords a copolymer having slight conductivity and
accelerating exchange of charges among toner particles thereby to make the
charge distribution narrow and sharp. If only the hydrophobic monomer
having a charge control group is adhered to the capsule shell, the
resulting toner particles hardly exchange charges among them, resulting in
a broad charge distribution.
If a copolymer of a hydrophilic monomer and a hydrophobic monomer is
directly adhered to the surface of core particles without coating the
surface with a substance capable of forming a radical, since the core
particles generally comprise a hydrophobic substance, they have good
adhesion to the segment derived from the hydrophobic monomer but poor
adhesion to the segment derived from the hydrophilic monomer. As a result,
substances constituting the core particles tend to ooze out to cause
contamination or agglomeration of toner particles. According to the
present invention, the core substances can be prevented from oozing by the
coat of a substance capable of forming a radical.
The present invention is now illustrated in greater detail with reference
to Examples, but it should be understood that the present invention is not
deemed to be limited thereto. All the percents and parts are by weight
unless otherwise indicated.
EXAMPLE 1
(1) Preparation of Capsule Particles
In a mixed solvent of 60 g of dibutylnaphthalene and 60 g of ethyl acetate
were dissolved 30 g of polyisobutyl methacrylate (Mw=16.times.10.sup.4)
and 40 g of a styrene-n-butyl methacrylate copolymer
(Mw=6.times.10.sup.4). To the solution was added 120 g of a magnetic
powder "EPT-1000" (produced by Toda Kogyo K.K.), and the mixture was
dispersed in a ball mill for 16 hours. To 200 g of the resulting
dispersion were added 30 g of an isocyanate "Sumidur L" (produced by
Sumitomo Bayer Urethane K.K.) and 24 g of ethyl acetate, followed by
thoroughly mixing. The resulting liquid was designated liquid A.
Separately, 10 g of hydroxypropylmethyl cellulose "Metholose 65H50"
(produced by Shin-etsu Chemical Industry Co., Ltd.) was dissolved in 200 g
of ion-exchanged water, followed by cooling to 5.degree. C. The resulting
liquid was designated liquid B.
Liquid B was agitated in an emulsifier "Autohomomixer" (manufactured by
Tokushuki Kako K.K.), and liquid A was slowly poured therein to conduct
emulsification to prepare an O/W emulsion of oil droplets having a mean
particle size of about 12 .mu.m. The emulsion was then stirred in a
stirrer equipped with a propeller blade "Three-One Motor" (manufactured by
Shinto Kagaku K.K.) at a speed of 400 rpm. Ten minutes later, 100 g of a
5% diethylenetriamine aqueous solution was added thereto dropwise. After
completion of the dropwise addition, the mixture was heated to 60.degree.
C. for 3 hours to conduct encapsulation. After completion of the reaction,
the reaction mixture was poured into 2 liters of ion-exchanged water,
thoroughly stirred, and allowed to stand. The supernatant liquor was
removed, and the sedimented capsule particles were repeatedly washed with
ion-exchanged water 7 more times in the same manner as above.
Ion-exchanged water was added to the finally obtained capsule particles
containing an oily binder encapulated with a polyurea resin to prepare a
capsule suspension having a solids content of 40%.
(2) Preparation of Toner
To 125 g of the capsule dispersion prepared in (1) above (corresponding to
50 g of capsule particles) was added 125 g of ion-exchanged water, and the
mixture was stirred in a stirrer "Three-One Motor" at a speed of 200 rpm.
Five grams of 1N nitric acid and 4 g of a 10% cerium sulfate aqueous
solution were added thereto, and 0.5 g of ethylene glycol dimethacrylate
was then added thereto, followed by reacting at 15.degree. C. for 3 hours.
After completion of the reaction, the reaction mixture was poured into 1
liter of ion-exchanged water, thoroughly stirred, and allowed to stand.
The supernatant liquor was removed, and the sedimented capsule particles
were repeatedly washed 2 more times in the same manner as above to obtain
capsule particles having ethylene glycol dimethacrylate graft-polymerized
on the outer shell thereof. The resulting capsule particles were
re-suspended in ion-exchanged water and stirred in Three-One Motor at a
speed of 200 rpm. To the mixture were successively added 0.4 g of
potassium persulfate, 0.1 g of triethylammoniumethyl methacrylate
chloride, 1 g of methyl methacrylate, and 0.16 g of sodium
hydrogensulfite, followed by allowing the mixture to react at 25.degree.
C. for 3 hours. After completion of the reaction, the reaction mixture was
poured into 2 liters of ion-exchanged water, thoroughly stirred, and
allowed to stand. The supernatant liquor was removed, and the sedimented
capsule particles were repeatedly washed 4 more times in the same manner
as above to obtain capsule toner particles having triethylammoniumethyl
methacrylate chloride and methyl methacrylate graft-copolymerized on the
outer shell thereof. The resulting capsule suspension was spread in a
stainless steel-made vat and dried in a drier (produced by Yamato Kagaku
K.K.) at 60.degree. C. for 10 hours.
(3) Evaluation Test
Three grams of the capsule toner obtained in (2) above and 100 g of an iron
powder carrier having coated thereon a phenolic resin were mixed in an
atmosphere of 20.degree. C. and 50% RH. The quantity of charge of the
capsule toner was found to be 20 .mu.C/g as measured by a blow-off method
(hereinafter the same). When the mixing was conducted in an atmosphere of
28.degree. C. and 80% RH, the charge quantity was 19 .mu.C/g, and the
charge distribution was proved sharp. Then, 100 parts of the toner was
sufficiently mixed with 1 part of hydrophobic silica "RA200H" (produced by
Nippon Aerosil K.K.), and subjected to copying test under a high
temperature and high humidity condition (35.degree. C., 85% RH) by the use
of a copying machine ("2700" manufactured by Fuji Xerox Co., Ltd. and
modified for capsule toners; reversal development). As a result, 20,000
copies free from fog were obtained in a stable manner.
COMPARATIVE EXAMPLE 1
Capsule toners having triethylammoniumethyl methacrylate chloride
graft-polymerized on the outer shell thereof were produced in the same
manner as in Example 1, except for replacing 0.1 g of
triethylammoniumethyl methacrylate chloride and 1 g of methyl methacrylate
with 1 g of triethylammoniumethyl methacrylate chloride. Three grams of
the resulting capsule toner were mixed with 100 g of an iron powder
carrier having coated thereon a phenolic resin were mixed in an atmosphere
of 20.degree. C. and 50% RH. The quantity of charge of the capsule toner
was found to be 10 .mu.C/g. When the mixing was conducted in an atmosphere
of 28.degree. C. and 80% RH, the charge quantity was 4 .mu.C/g. Then, 100
parts of the toner was sufficiently mixed with 1 part of hydrophobic
silica "RA200H", and subjected to copying test in the same manner as in
Example 1. As result, images obtained from the 1,000th copy suffered from
fog, and the 2,000th copy had a reduced image density, seriously lacking
clearness.
EXAMPLE 2
Capsule toners having vinylidene chloride and methacrylic acid
graft-polymerized on the outer shell thereof were produced in the same
manner as in Example 1, except for replacing 0.1 g of
triethylammoniumethyl methacrylate chloride and 1 g of methyl methacrylate
with 0.95 g of vinylidene chloride and 0.5 g of methacrylic acid. Three
grams of the resulting capsule toner were mixed with 100 g of an iron
powder carrier having coated thereon a phenolic resin were mixed in an
atmosphere of 20.degree. C. and 50% RH. The quantity of charge of the
capsule toner was found to be -25 .mu.C/g. When the mixing was conducted
in an atmosphere of 28.degree. C. and 80% RH, the charge quantity was -23
.mu.C/g, and the charge distribution was proved sharp. Then, 100 parts of
the toner was sufficiently mixed with 1 part of hydrophobic silica
"RA200H", and subjected to copying test in the same manner as in Example
1. As result, 20,000 copies free from fog were obtained in a stable
manner.
COMPARATIVE EXAMPLE 2
Capsule toners having vinylidene chloride graft-polymerized on the outer
shell thereof were produced in the same manner as in Example 2, except for
replacing 0.95 g of vinylidene chloride and 0.5 g of methacrylic acid with
1 g of vinylidene chloride. Three grams of the resulting capsule toner
were mixed with 100 g of an iron powder carrier having coated thereon a
phenolic resin were mixed in an atmosphere of 20.degree. C. and 50% RH.
The quantity of charge of the capsule toner was found to be -25 .mu.C/g
with a very broad charge distribution. When the mixing was conducted in an
atmosphere of 28.degree. C. and 80% RH, the charge quantity was -23
.mu.C/g with a very broad charge distribution. Then, 100 parts of the
toner was sufficiently mixed with 1 part of hydrophobic silica "RA200H",
and subjected to copying test in the same manner as in Example 1. As
result, copies obtained from the very beginning suffered from fog, and the
1,000th copy had a reduced image density, seriously lacking clearness.
As described and demonstrated above, the electrophotographic toner
according to the present invention comprises a core particle and an outer
shell having adhered thereon a copolymer containing a hydrophilic monomer
having a charge control agent and a hydrophobic monomer or a copolymer of
a hydrophobic monomer having a charge control agent and a hydrophilic
monomer. Attributed to such a structure, stability of chargeability
against environmental changes and sharpness of charge distribution can be
enhanced.
While the invention has been described in detail and with reference to
specific examples thereof, it will be apparent to one skilled in the art
that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
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